The present invention relates to electronic circuits, and more specifically to a system for controlling a fan.
To achieve high resolution fan control, the system controlling the fan needs to be able to adjust the fan speed at a high resolution. One way to achieve this is by adjusting the Pulse Width Modulation (PWM) Duty Cycle to get the desired fan speed.
The preferred PWM frequency (driving the fan) is above 20 KHz with a variable duty cycle for adjusting the fan speed. The minimum 20 KHz frequency is chosen because the audio range of human is from 200 Hz up to possibly 20 KHz. Therefore, any frequency above 20 KHz is typically not heard.
For most thermal management solutions in a system, the fan speed is determined primarily by temperature inputs of the system. Thermal Management Systems usually require relatively lower frequency clock (hundreds of KHz typically) due to noise and power consumption requirements. This clock frequency does not allow enough resolution (8-bit or more) for relatively high frequency (greater than 20 KHz) PWM fan control.
Typical solutions require faster clock frequency for high resolution high frequency PWM. What is needed is a way to generate a high resolution high frequency PWM signal with a low input clock frequency.